1. Field of the Invention
The present invention relates to a light-emitting element and a light-emitting device and, particularly, to a semiconductor light-emitting element and a light-emitting device in which a semiconductor material is used.
2. Related Art
Semiconductor light-emitting elements are widely used in display devices, lighting devices, recording devices, etc. Particularly, semiconductor light-emitting diodes (LEDs) which do not use stimulated emission are used as display devices because of their high luminance. As a recent new application, trials have been made to use an LED as a lighting device in which an LED and a fluorescent material layer are combined (refer to the Japanese Patent Laid-Open No. 2004-179644, for example). This publication discloses a fluorescent-material laminated structure in which two kinds of fluorescent material layers are laminated on a semiconductor light-emitting element such as an LED, in order to increase color rendering properties, and a light-emitting device of white color etc. in which this fluorescent-material laminated structure is used. In the fluorescent material layers of this light-emitting device, a diffusion agent, a binder resin and a fluorescent material are blended by being adjusted. This increases luminous efficiency and suppresses the deterioration of the fluorescent material layers.
In the conventional light-emitting device described in the above-cited publication, the lighting device in which an LED and fluorescent material layers are combined intends to improve the luminance of the lighting device by contriving the material and structure of the fluorescent material layers. However, the conventional technique is sufficient for use in a lighting device. That reason will be described below.
LEDs are excellent in high efficiency and small heat generation, compared to the existing electric lamps. Therefore, it is assumed that the existing electric lamps will be more and more replaced in the future by combinations of an LED and a high-luminance fluorescent material layer. On the other hand, compared to fluorescent lamps which are widely used as lighting devices, LEDs have still problems in efficiency, heat generation and operating power source, and even when high-luminance fluorescent material layers are used, it will be practically difficult to obtain an excellent luminous efficiency (luminous efficiency relative to input power) enough to replace the fluorescent lamps. Thus, conventional LEDs have the problem that they are not sufficient in terms of efficiency, heat generation and operating power source and that it is difficult to obtain an excellent luminous efficiency enough to replace the fluorescent lamps which are widely used as lighting devices.